1. Field of the Invention
The present invention generally relates to semiconductor wafer processing, and more particularly to methods and associated apparatus for handling semiconductor wafers and wafer-like objects.
2. Description of the Related Art
In a semiconductor wafer processing system, semiconductor wafers are transferred from one station to another using a manipulator such as a robot. A typical robot used in the semiconductor industry has a body, an arm, and an end-effector attached to the arm. The end-effector is the part of the robot that supports a wafer.
Conventional end-effectors are ineffective in supporting flexible and/or deformed wafers. For example, end-effectors employing vacuum suction do not adequately support a deformed wafer because vacuum sealing requires a relatively flat surface. End-effectors that support a wafer from the bottom by gravity are also ineffective because deformed wafers have unpredictable shapes, and thus cannot provide an end-effector a consistent bottom surface contact area.
End-effectors utilizing the Bernoulli principle are likewise inadequate to support wafers that are not relatively flat. Existing Bernoulli end-effectors can only accommodate 1 to 2 millimeters (mm) of deformation for every 150 mm of length whereas wafer deformation can exceed 8 mm as substrates and deposited films get thinner.
PCT Application WO 97/45862, published Dec. 4, 1997 shows an end-effector that uses vortex chucks to support a wafer. While the end-effector in the aforementioned PCT application is generally more effective in handling flexible wafers than current non-vortex designs, that end-effector does not have, at least, an effective means for detecting and supporting very thin, flexible wafers.
The present invention relates to a method and associated apparatus for handling relatively non-flat wafers and wafer-like objects. The invention can be employed in a semiconductor wafer processing system and generally for transporting objects including flat panel displays, very thin wafers, and deformed wafers.
An end-effector in accordance with one embodiment includes multiple vortex chucks for supporting a wafer. Vortex chucks are located along the periphery of the end-effector to help prevent a flexible wafer from curling. The end-effector has limiters to restrict the lateral movement of the supported wafer.
In one embodiment, the limiters are retractable to allow the end-effector to press a supported wafer against a surface (e.g., sticky tape). In one example, the limiters are spring loaded pins which retract as the end-effector presses the supported wafer against the surface.
In one embodiment, an edge of the end-effector is chamfered to prevent a flexible wafer from contacting a sharp portion of the end-effector.
In one embodiment, the end-effector has an outline which follows that of the center cut-out portion of a conventional wafer cassette to increase the area of the end-effector for supporting a wafer.
In one embodiment, the end-effector has a detector for detecting the presence of a wafer. The detector is mounted at a shallow angle to allow the end-effector to be positioned close to a wafer to be picked-up, thereby allowing detection of deformed wafers contained in a wafer cassette. The shallow angle of the detector also minimizes the thickness of the end-effector.
A wafer station in accordance with one embodiment includes multiple vortex chucks for supporting a wafer. Vortex chucks are located along the periphery of the station to fully support a flexible wafer.
In one embodiment, the top surface of the wafer station is very flat and has a very smooth finish so that a wafer that is curled down can be picked-up from the station without damaging the edges of the wafer as the wafer curls up during the pick-up step.
In one embodiment, the wafer station has a hole in the middle to accommodate various detectors for detecting the presence of a wafer.
These and other features of the invention will be apparent to a person of ordinary skill in the art upon reading the following detailed description and figures.